1. Field of the Invention
The present invention relates generally to an apparatus for thermal welding of overlapped sheeting, and more particularly, to a self-propelled machine for welding thermoplastic sheet material by the application of heated air.
2. Description of the Related Art
The use of thermoplastic roofing material in sheet form has become increasingly popular. Such roofing material, which is generally of PVC plastic or the like, is laid on a roof from rolls of the material. Adjoining edges of the sheet material are overlapped and welded by the application of heat to provide watertight seams. The resulting roof offers durable long-lasting protection at relatively little expense and with little maintenance.
Various devices are known for welding the overlapped seams of thermoplastic material. One example of a seam welding device is disclosed in Stevenson et al. U.S. Pat. No. 4,440,588 entitled "Hot Air Welder for Welding Roofing Material". The disclosed apparatus includes a blower communicating with a heater assembly mounted on a chassis which includes a pressure wheel and a tracking wheel. The welder accommodates inside and outside seams and has an air dam. A constant speed blower controlled by a gate valve controls the amount of air to the heater assembly. An alarm is provided for sensing insufficient temperature of the heater during operation of the welder.